Soils, Soil Characteristics and Factors Affecting Management

What is Soil? Mineral - Sand, Silt, Clay Pore Space 25%

Water 25%

Organic Matter Organic Matter 5%

Mineral Matter 45%

-Decomposed Plants - Decomposed Microorganisms -Decomposed Animal Material

Soil Profiles • Note difference in top soil depth, organic matter, color and clay content

Harney soil

Harney silt loam

Factors Involved In Soil Formation z Climate z Parent Material z Ecology (plant and animal life) z Slope z Time

Average Annual Precipitation

Soil Microorganisms z N fixation in legume crops (Rhizobium) z Decompose organic materials ¾ Crop residues ¾ Organic chemicals

z Diseases z Mineralize and immobilize nutrients

Soil Microorganisms Amount of organisms in top foot of soil Organism

Number/gram soil

Typical Pounds/acre-foot soil

Bacteria

1 Billion

750

Actinomycetes

15 Million

1,100

Fungi

1 Million

1,700

Protozoa

1 Million

300

Algae

100,000

250

Yeasts

1,000

---

Worms and Insects

---

900

T.M. McCalla, Neb. Ag. Exp. Sta. Research Bulletin, 1959

Soil Microbes Mineralize and Immobilize Plant Nutrients. Inorganic nutrients

Organic nutrients Plant Unavailable Form

Mineralization

Immobilization

Plant Available Form

‘Biological Activators’ z With few exception, they do not work z Soil microbe population resistant to change z Best way to stimulate soil microbes is to provide high levels of organic residues z Fertilizers generally beneficial to soil microbes

Why Soils Vary in Productivity z Soils tend to be vary greatly in chemical and physical properties even within fields that appear uniform z This variability is the source of the interest in intensive soil sampling and variable rate technology z Let’s look at soil properties that affect crop production

Soil Physical Properties Affecting Soil Productivity Dr

ain a

ge

Depth of Rooting Zone

e r tu

Color S

c u tr

Texture

Soil Productivity

Po ro

e p Slo

Permeability

sit y

Depth of Rooting Zone Crop

Rooting Depth

Major Feeding Zone

Wheat

4 - 6 ft.

80% in top 3 ft.

Corn

4 - 7.5 ft.

75% in top 2 ft.

Grain Sorghum

4.5 - 6 ft.

75% in top 3.5 ft.

Alfalfa

20 ft. +

50% in top 3.5 ft.

Bromegrass

5.5 - 6.5 ft.

75% in top 3.5 ft.

Weaver, Root development of field crops

Soil Structure •The arrangement of soil particles into larger units •Structure affects soil permeability, porosity and root growth •Affects resistance to surface crusting Structure is destroyed by ? Structure is improved by ?

Kinds of Soil Structure Crumb

Desirable

Platy (less desirable)

Granular

Bulk Density • The weight of a unit volume of soil, including any air space and organic materials. • Average soil bulk density for a cultivated loam is 68 to 87 lb/cu ft or 1.1 to 1.4 g/cu cm • Soils compacted will have higher bulk densities • Good growth below 87 lb/cu ft for clays and 98 lb/cu ft for sands

Soil Porosity and Permeability •

Porosity is the total amount of pore space in the soil (30 to 60%) – Affects the storage of air and water – Affects the rate of movement of air and water

•

Permeability is the ease in which water, air, and plant roots move through the soil – Ease of air, water and root movement – Affects rate of water intake and drainage

•

Porosity and permeability are affected by soil texture, structure, organic matter and compaction

Soil Textural Triangle

CLAY LOAM

SANDY CLAY LOAM

t Sil

SILTY CLAY

nt

CLAY

SANDY

CLAY

rce

Pe rce n

Pe

tC lay

100 0

SILTY CLAY LOAM

LOAM SILT LOAM SANDY LOAM LO AM Y SA ND SAND

SILT

100

0 100

0 Percent Sand

SOIL TEXTURE AS DEFINED BY SOIL TEXTURAL CLASS AND ESTIMATED BY A HAND-FEEL METHOD SOIL TEXTURAL GROUP

SOIL TEXTURAL CLASS

Coarse

Sand Loamy Sand

Feels gritty does not leave a very coarse ribbon or smear on hand.

Sandy loam

Feels gritty does not leave coarse ribbon, breaks into small pieces.

Medium

Loam Silt Loam Silt Sandy clay loam

Feels smooth and flour-like, does not ribbon, breaks into pieces about 1/2 inch long or less

Fine

Silty clay loam Clay loam

Forms ribbon that breaks into pieces about 3/4” long

Sandy clay Silty clay Clay

Forms long pliable clay ribbons 2” or longer

FEEL

Comparative Size of Sand, Silt and Clay Sand Silt

2.00-0.05mm

0.05-0.002mm

Clay Less than 0.0002mm 10 mm

Clay Surface Area 1,000X equal weight of Sand Acre plow depth equals the surface area of the U.S.A.

Types Of Soil Clay z Kaolinite ¾ Lower CEC and water holding capacity ¾ Not a shrink/swell clay ¾ Dakota Sandstone formation in central Kansas

z Montmorilinite ¾ Predominant clay in Kansas ¾ High shrink/swell – ‘gumbo’ if high clay content ¾ High CEC and water holding capacity

z Illite ¾ High potassium soils ¾ Good tilth, water holding capacity ¾ No shrink/swell

Soil Water EXCESS OR GRAVITATIONAL: amount of water between saturation and field capacity. AVAILABLE SOIL WATER: water held by capillary forces between field capacity and permanent wilting point. Saturation -Readily Drained Water

100% Available Water Capacity 0%

Field Capacity - Water Managed by irrigation scheduling Minimum Balance -Water available to plant under stress Permanent Wilting - Water Unavailable to plants

Unavailable Water Oven Dry

Soil Moisture Holding Capacity Water is attracted to soil particles and held as a film against the pull of gravity. Water closest to the soil particle is held the most tightly. At field capacity gravity drainage has ceased. Pore Space Water Film

Soil Particle Forces of Surface Tension

Soil Moisture Holding Capacity At permanent wilting point soil clay particles have greater affinity for water than plants ability to compete.

Wilting Point Plant Root

Water Film

Soil Particle Forces of Surface Tension

Water holding Capacity as Affected by Soil Texture

Inches water/ft. soil

5

y

d

Fiel

4

c it a p Ca

3

Av

2

1

Per Sand

le b a ail

nt e n ma

ter a W

g n i t l Wi

Sandy Loam Silt Loam

ge a t n e Perc

Clay Loam

Clay

Crop Corn Grain Sorghum Sunflower Winter Wheat Soybean

Maximum ET Full-season Variety

Threshold ET

Yield vs. ET

Long-term Yield vs. ET

inches water

inches water

bu/acre/inch

bu/acre/inch

25 21 22 23 23

10.9 6.9 5.4 10.1 10.0

16.8 12.2 220 * 6.0 5.5

12.6 9.1 150 * 4.5 4.25

Source: L. Stone, Kansas State University, 15th Central Plains Irrigation Conference Proceedings, Feb. 4-5, 2003, Colby, KS

Crop Corn Grain Sorghum Sunflower Winter Wheat Soybean

Maximum ET Full-season Variety

Threshold ET

Yield vs. ET

Long-term Yield vs. ET

inches water

inches water

lb grain/inch

lb grain/inch

25 21 22 23 23

10.9 6.9 5.4 10.1 10.0

941 683 220 360 330

706 510 150 270 255

Source: L. Stone, Kansas State University, 15th Central Plains Irrigation Conference Proceedings, Feb. 4-5, 2003, Colby, KS

Available Water For Several Kansas Soils Soil Type

Depth

Available Water

Permeability

Inches

inches/foot of soil

Inches/hour

0-7

2.2

0.2-0.3.

7-18

2.2

0.2-0.3.

18-26

2.2

0.1-0.2

26-60

2.2

0.2-0.4

0-6

2.2

0.2-0.4

6-34

2.2

0.2-0.4

34-60

2.2

0.2-0.4

Pratt loamy fine sand

0-70

1.4

2.0-5.0

Wymore silty clay loam

0-6

2.6

0.2-0.6

6-26

1.6

0.06-0.2

26-60

2.3

0.2-0.6

0-14

2.4

0.6-2.0

14-60

2.2

< 0.06

Harney silt loam

Richfield silt loam

Parsons

Erosion • Erosion moves detached soil particles by wind or flowing water

Detachment • Detachment separates individual soil particles from the soil matrix, e.g. by impact from raindrops, other soil particles, hooves or wheels

Soil Erosion by Water 9 Sheet erosion - soil is eroded uniformly across a slope 9 Rill erosion - numerous tiny gullies (rills) randomly occur 9 Gully erosion - with increased rainfall duration and intensity, runoff volumes increase and concentrate in small ravines

Sheet/Rill Erosion

Rill Erosion

Gully Erosion

Universal Soil Loss Equation (RUSLE) Erosion (ton/a) = R * K * LS * C * P R.... Climate (rainfall index) K.... Soil Erodibility Factor LS .. Slope Steepness & Length P..... Soil Surface Conditions / Practices C.... Vegetative Cover

Wind Erosion

Westcentral-Northwest Kansas Memorial Weekend, 2004

Westcentral-Northwest Kansas Memorial Weekend, 2004

Wind Erosion • Similar to water, except wind becomes transports Three types of movement: 1. Suspension 2. Saltation 3. Surface Creep

• Once soil particles begin to move, they have abrasive action on the soil surface, and break down soil aggregates.

Wind Erosion Sandy soils are most susceptible to wind erosion because usually poorly aggregated (less O.M., clay to form aggregates) Conditions conducive to Wind Erosion: * Poorly Aggregated * Bare Soils * Loose Surface * Dry Prevention of Wind Erosion: * Windbreaks * Crop Residues * No-till * Stubble Mulch

Ground Cover Reduces Erosion

Soils, Soil Characteristics and Factors Affecting Management

Review Exercises 1. Which of the following is not a major factor affecting soil development and its eventual productivity: a. c.

Climate. Native wildlife.

b. d.

Parent material. Native vegetation.

2. For optimum plant growth conditions, a desirable surface soil should have approximately _____% pore space for air and water. a. b. c. d.

15. 35. 50. 75.

3. The following is a parent material deposited by wind: a. b. c. d.

Alluvium. Loess. Glacial till. Colluvium.

4. As a general rule, most potassium deficient soils and those requiring lime occur in humid regions receiving in excess of about 30" of annual precipitation. a. True. b. False. 5. Subsoil fertility does not contribute significantly to a crop's nutritional requirements. a. True. b. False. 6. A fertile soil is always a productive soil. a. True. b. False.

. Soil structure has considerable influence on soil: a. Porosity. b. Permeability. c. Drainage. d. All of the above. e. None of the above.

. Of the three size classes of mineral particles comprising soil texture (sand, silt, and clay), only silt contributes significantly to soil fertility.

a. True. b. False

. Sand particles are primarily composed of:

1. A silt loam soil can typically provide plants about _____" of available water per foot of soil.

a. 1. b. 2. c. 4. d. 5.

2. Organic matter is an important contributor of all of the following nutrients: potassium, nitrogen, phosphorus, and sulfur for good plant nutrition.

a. True. b. False.

4. Which of the following does not have a significant influence on organic matter content: a.

Temperature and precipitation..

b. Drainage. c. Slope and erosion. d. Bulk density.

5. Fertilizer generally has a positive effect on soil microorganisms by providing nutrients and increasing crop residues. a. True

b. False

6. An acre of soil to a tillage depth of 6" to 7" weighs approximately __________ lb (see Page 17).

7. Soil is most subject to compaction when the soil moisture content is: